Recent heavy rainfall causes the slips of a river levee in several of sites in Japan. The reason for these slips are said to be the rainwater drainage from its crest pavement. This research focused on the mechanism of these slips with the effect of vegetation rootstock. Model experiments were conducted to observe the mechanism. It has been clarified from the results that if the amount of rootstock in the unit volume of surface soil is high, the possibility of slip become low. On the contrary, the tendency of slip become higher in case that the depth of surface soil with rootstock is deep.
